The buoyancy control system for tubes including a buoyancy control material of a density equal to or greater than 2000 kg/m3 that comprises components as follows: cementing component, additive regulating the solidification time, fillers—water-sand mixture and/or water-barite mixture (U.S. Pat. No. 6,663,453, F16L 1/16, 9 Jan. 2003), is known. The description of this patent does not disclose a component content of the buoyancy control material and a grain-size composition of fillers. The fact that acceptable density of buoyancy control material of present-day main pipelines is considerably higher than 2000 kg/m3 is a disadvantage of the known system.
Extra heavy concretes, among them barite concrete, a density of which exceeds 2500 kg/m3 (http://betony.ru), are known, but a composition of extra heavy concrete and details of its application as a buoyancy control material for tubes are not described in the abovementioned source.
The concrete comprising barite as a filler is referred to (WO 98/01402, C04B 14/36, 15 Jan. 1998). To increase density, the filler has the predetermined grain-size composition, in which 8% wt (percents by weight) of barite are in the form of extra fine fraction having a particle size from 0.01 μm to 1000 μm, 4% wt in the form of fine fraction having a particle size from 1 mm to 3 mm, 10% wt in the form of coarse fraction having a particle size from 3 mm to 7 mm; fine silica sand having a grain size from 0.1 mm to 3 mm; coarse fraction of gravel from 3 mm to 75 mm. A water-cement ratio by mass is specified within the range from 0.30 to 0.35. Such composition has two major disadvantages: first—impossibility to obtain buoyancy control material with the guaranteed density exceeding 2800 kg/m3 due to lack of limitations by materials and their density for coarse and fine fillers; second—a small water-cement mass ratio in solution (from 0.30 to 0.35), that does not allow to use sluggish solution having coarse fractions to fill up the annulus between the conductive pipe and shell by injection through openings in lids.
The buoyancy control material for subsea main pipelines, that is the nearest analog of the claimed invention and contains cement, filler, plasticizing agent and water (RU 2257503, F16L 1/24, 27 Jul. 2005), is known. This material is employed to form a layer of a buoyancy control material on a conductive pipe by filling in the annulus between the conductive pipe and shell of main pipelines and is the cement-sand solution with a mobility being sufficient to fill in the annulus between the conductive pipe and shell. The major drawback of the known material is its low density (up to 2400 kg/m3) generating a need to increase sizes of the buoyancy control material annulus to make a pipeline negatively buoyant.